Training devices designed to be struck by an athlete's hands or feet are well known in the prior art. A very few of these devices are adapted to provide the user with an indication of how effectively his or her blow has struck the device for providing the athlete with feedback on his or her performance to allow the user to improve his or her technique.
A punching bag which provides feedback to the user concerning impact force is described in U.S. Pat. No. 4,208,048. This device includes an air bladder mounted on the exterior of a punching bag. The air bladder is connected to a pressure gauge. When the athlete strikes the bladder, pressure inside the bladder rises. The pressure rise is communicated to the athlete on the gauge. This device has several deficiencies. First, it is difficult to maintain constant internal pressure in the bladder, as leakage can be expected due to repeated impacts over a period of time. In addition, the pressure in the bladder can vary with changes in ambient temperature, as well as with temperature changes that result from repeated impacts. Another problem is that conventional air pressure gauges may not provide sufficiently fast response to obtain a true indication of the force of the impact.
Another device which provides an athlete feedback concerning impact force is shown in U.S. Pat. No. 4,330,119. This patent also employs a bag inflated with air and a pressure gauge readout. This device can be expected to have the same deficiencies as the device shown in U.S. Pat. No. 4,208,048. In fact, bags made according to the foregoing patent have been found to yield inaccurate readings due to temperature changes and air leakage from the bag.
The athletic bag shown in U.S. Pat. No. 4,527,796 is an inflatable bag holding pressurized air over a reservoir of water. A sensor detects the rise in air pressure and givs a readout proportional to the impact. The problem with systems of this type is that air pressure is subject to changes of temperature and repeated impacts tend to cause air leakage. Further, the presence of air in the bag would likely cause the water to "slush", causing extraneous signals at the sensor which effect the accuracy of the readout. This internal turbulence in the bag could be expected to be particularly problematic when the athlete strikes the bag rapidly and repeatedly. Another draw back of this system is that the sensor must be compatible with both air and water due to the likelihood that water will reach the sensor.
Another system for detecting and indicating the strength of an impact was described in the January 1979 issue of Karate Magazine. This system uses a leather bag completely filled with water to a slight over pressure. The bag has an internal pressure transmitter. A signal from the internal pressure sensor is displayed at an external readout to provide the athlete with feedback. A problem that can be expected is that residual waves or vibrations inside the bag would produce extraneous signals which would adversely effect the sensor readings, particularly when the bag is struck in rapid succession.
A shortcoming of all fluid filled bags used particularly by practitioners of the martial arts is the low comfort factor; that is, it doesn't have the right "feel" as compared to foam-filled bags and the like. Fluid filled bags are usually too resilient, and the user's hands or feed rebound too quickly than most martial arts practitioners would like.
Thus, there exists a need for athletic training apparatus which receives an impact from an athlete, and which provides an accurate indication of the velocity, force, frequency and/or energy of the impacts. There further exists a need for such an apparatus that is suitable for measuring fast and repeated blows. There further exists a need for an apparatus for measuring blows which is more reliable, less sensitive to changes and temperature, and more readily transportable than existing apparatus.